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Intensified irrigation threatens agricultural productivity

High concentrations of salt in agricultural soil is an environmental problem that has plagued human civilization from its very beginning. Also in modern times, salinization of soils is a problem restricting agricultural productivity.

Irrigation can make areas suitable for agriculture that would otherwise be too dry to support high crop yields. However, water used for irrigation of fields evaporates and leaves behind dissolved salts, which over time accumulate in the soil to levels that negatively affect growth of crop plants.

In order to achieve food security amidst a growing population, agricultural productivity will have to be increased. Much of the projected population growth is going to take place in parts of the globe that experience low rainfall year-round or seasonally. Agriculture in these regions is heavily reliant on irrigation and many areas are already suffering from soil salinization. As irrigation agriculture intensifies, areas with salt-affected soils will increase.

Soil salinization affects microorganisms
For plants to be able to grow, they need the support of huge numbers of microorganisms that live in soil. Microorganisms, such as bacteria and fungi, are important as decomposers of dead organic material. Through their activity as decomposers, microorganisms drive the biogeochemical cycling of carbon and nutrients in soil that is necessary to sustain life on earth.

PhD-student Kristin Rath has studied the soil salinization impact on microorganisms, and the impact on processes carried out by microorganisms. Her research shows that all of these processes are strongly inhibited by salt. Bacteria are particularly sensitive to salt exposure, while fungi could maintain comparatively higher growth rates.

Areas in which saline soils are common often undergo periods during which soils dry out. Drying also inhibits microbial activity in soils and in saline soils the combined impact of salinity and drying could make the effects of the individual factors worse.

- I tested dry soils of different salinity and found that indeed microorganisms were affected more strongly by drying if soils were also saline, says Kristin Rath.

After rewetting dried soils to the initial moisture levels, growth and respiration commenced immediately in less saline soils, while in saline soils a lag period of several hours occurred, during which respiration and growth were very low.

- As salt-affected soils are becoming an increasing problem in agriculture, the ability of microorganisms in saline soils to uphold important functions needs to be considered, Kristin Rath concludes.

Kristin Rath is defending her thesis Soil salinity as a driver of microbial community structure and functioning on Friday January 19.

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